It lets you pick out potentially useful worlds for further investigation, and then further-investigate them. It's a good RP endeavor with practical benefits. I don't think it was ever really intended as something you should do for every dead rock. In Aurora-VB, i only team survey potential colonies and bodies that already have notably good minerals.
In Aurora-C, it could also potentially have impact on ship design, and on player behavior. Right now, optimal play essentially involves throwing out lots of expendable survey ships because they really arn't worth the fuel or effort of naval squadrons to even pretend to protect them. A large science vessel worth many BP and carry as much as 10 or more commanders would in comparison be an asset of considerable worth. Or, difficulty of survey could be split up between 'asteroidal' - easy - and 'planetary' - much more difficult'.
Consider that surveying is somewhat degenerate right now in Aurora VB. There's little consideration of systems too far to practically survey - little use of forward survey bases - no percentage in protecting your survey ships. It's unappealing micro precisely because there's little reward or engagement in the mechanic right now.
Except as you point out, there's no reason not to fully survey every rock, because distance is otherwise a large obstacle. Better to have 100 minerals in a colonized system system than 1000 ten jumps away. So in practice geosurvey teams/ground units always boil down to "the optimum path is lots of unnecessary micromanagement".
As for the rest, I'm not opposed to survey ships being more expensive, I'm opposed to having to survey things
twice to get the full results. Not to mention two levels of survey wouldn't change what you're saying; if there were cheap initial survey ships and expensive secondary survey ships, people would just explore systems with the cheap ones and only send in an expensive one once the system was checked out (and thus wouldn't need an escort).
If you want actual reasons to escort them, or establish frontier bases, you'd want expensive survey ships but only one survey level.